Aquila Pieces: Coins used during the Great Crusade (Horus Rising (Novel), Chapter 5) and Horus Heresy in various denominations, including a Five Aquila Piece, which was about the same size as a Throne (Garro (Novel), Chapter Five).
Credits: Used on Necromunda in M41 (Necromunda: Outlanders Rulebook, pg. 66).
Crowns: Used from the Great Crusade (Legion (Novel), Chapter 2), to Karoscura in M41 (The Strange Demise of Titus Endor (Short Story)).
Ducats: Golden trade coins issued by Navigator Houses able to be used as currency wherever their ships travelled in M41 (Farseer (Novel): Chapter Five).
Estrillian Newmarks: Used on Atraxia. A tarot deck could potentially be bought for as few as 27 Newmarks (Baneblade (Novel), Interstitial between Chapters 14 & 15, pg. 229).
Terces: Silver coin, used on Medusa in M41 (Farseer (Novel): Chapter One).
Thrones: Gelt coins used from the Horus Heresy (Garro (Novel), Chapter Five), to the Calixis Sector in M41 (Dark Heresy Core Rulebook, pg. 124). About the same size as a Five Aquila Piece (Garro (Novel), Chapter Five).

Also, a single currency can have MULTIPLE NAMES. United States Dollars are called "Greenbacks", "Bucks", "Dollars", "Benjamins", "Bills", "Dough", "Tender", "Doubloons", "Moola", "Wad", and other things like that.

So what info we have from 'canon sources' already says that the Imperium as a whole does have at least one unified currency, even if local currencies also exist. And Crowns very much exist.

More importantly, there are organizations who's very presence/existence can MAKE that currency needed.

The Adeptus Mechanicus & The Adeptus Administratum being the two easiest examples.

If they say they want paid in "X" currency, they are either going to get paid in "X" currency, or make things difficult for that person/group until they start being paid in it.